When Ash is firing at the Possessed Woman near the beginning after the pit scene, he fires about four or five shots at her without reloading. And on the alternative ending in S-Mart he must have fired about 20 shots without loading new shells. Pretty Cool Shotgun.
Anyone who's seen Army of Darkness more than once knows that he doesn't have his shotgun while he's in S-Mart. That's why he breaks open a gun case and removes a rifle from it, which he then fires about 20 shots from. Super shotgun, indeed.
yeah... but his shot gun is double barrel, only 2 shots there.. The weapon he had in s-mart was a rifle, not a shotgun, but it is still funny s-mart would keep loaded weapons in their display case. Maybe he was from Texas? =P
Anyway, I don't think it was a slip-up. I would guess that most of what people would classify as slip-ups were either intentional during filming, or just left in for sh*ts and grins after the fact. Its a great movie.
Besides.. to get technical, wasn't the shotgun in ED2 only singly barrel?? I know it was in ED1, but I can't remember about ED2.
In the American version of ED3 The Army of Darkness, when Ash goes back to his own time and faces the deadite, if you watch, his clothes change when he takes the rifle out of the case and fires on the witch. The overkill and the clothes change are intentional an intentional homage to "The Rifleman".